The use of radiofrequency (RF) generators and electrodes to be applied to tissue for pain relief or functional modification is well known. For example, the RFG-3C plus RF lesion generator of Radionics, Inc., Burlington, Massachusetts and its associated electrodes enable electrode placement near target tissue and the heating of the target tissue by RF power dissipation of the RF signal output in the target tissue. For example, the G4 generator of Cosman Medical, Inc., Burlington, Mass. and its associated electrodes (such as the Cosman CSK electrode), cannula (such as the Cosman CC and RFK cannulae), and ground pads (such as the Cosman DGP-PM) enable electrode placement near target tissue and heating of the target tissue by RF power dissipation of the RF signal output in the target tissue. Temperature monitoring of the target tissue by a temperature sensor in the electrode can control the process. Heat lesions with target tissue temperatures of 60 to 95 degrees Celsius are common. Tissue dies and nerves are severed by sustained heating above about 45 degrees Celsius, so this process produces the RF heat lesion. RF generator output is also applied using a pulsed RF method, whereby RF output is applied to tissue intermittently such that tissue is exposed to high electrical fields and average tissue temperature are lower, for example 42 degrees Celsius or less.
RF generators and electrodes are used to treat pain, cancer, and other diseases. Related information is given in the paper by Cosman E R and Cosman B J, “Methods of Making Nervous System Lesions”, in Wilkins R H, Rengachary S (eds.); Neurosurgery, New York, McGraw Hill, Vol. 3, 2490-2498; and is hereby incorporated by reference in its entirety. Related information is given in the book chapter by Cosman E R Sr and Cosman E R Jr. entitled “Radiofrequency Lesions.”, in Andres M. Lozano, Philip L. Gildenberg, and Ronald R. Tasker, eds., Textbook of Stereotactic and Functional Neurosurgery (2nd Edition), 2009, and is hereby incorporated by reference in its entirety. A research paper by E. R. Cosman, et al., entitled “Theoretical Aspects of Radiofrequency Lesions and the Dorsal Root Entry Zone,” by Cosman, E. R., et al., Neurosurg 1984;15:945-950, describes various techniques associated with radio frequency lesions and is hereby incorporated by reference herein in its entirety. Research papers by S. N. Goldberg, et al., entitled “Tissue Ablation with Radio Frequency: Effect of Probe Size, Gauge, Duration, and Temperature on Lesion Volume,” Acad. Radiol., Vol. 2, pp. 399-404 (1995), and “Thermal Ablation Therapy for Focal Malignancy,” AJR, Vol. 174, pp. 323-331 (1999), described techniques and considerations relating to tissue ablation with radio frequency energy and are hereby incorporated by reference herein in its entirety. For a given electrode temperature, size of electrode, and time of heating, you can predict reliably ablation size as described in the papers entitled “Theoretical Aspects of Radiofrequency Lesions and the Dorsal Root Entry Zone,” by Cosman, E. R., et al., Neurosurg 15:945-950, 1984, and “Bipolar Radiofrequency Lesion Geometry: Implications for Palisade Treatment of Sacroiliac Joint Pain.” by E. R. Cosman Jr and C. D. Gonzalez, Pain Practice 2011; 11(1): 3-22 (hereinafter “Cosman and Gonzalez”), which are herein incorporated by reference in their entireties.
The use of high frequency (HF) electrodes for heat ablation treatment in the destruction of tumors is well known. One example is the destruction of cancerous tumors of the kidney using radio frequency (RF) heat ablation. A paper by D. W. Gervais, et al., entitled “Radio Frequency Ablation of Renal Cell Carcinoma: Early Clinical Experience,” Radiology, Vol. 217, No. 2, pp. 665-672 (2000), describes using a rigid tissue perforating and penetrating electrode that has a sharpened tip to self-penetrate the skin and tissue of the patient. This paper is hereby incorporated by reference herein in its entirety. A paper by Luigi Solbiati et al. entitled “Hepatic Metastases: Percutaneous Radiofrequency Ablation with Cool-Tip Electrodes,” Radiology 1997, vol. 205, no. 2, pp. 367-373 describes various techniques and considerations relating to tissue ablation with RF electrodes which are internally-cooled by circulating fluid, and is incorporated herein by reference. A paper by Rosenthal et al entitled “Percutaneous Radiofrequency Treatment of Osteoid Osteoma,” Seminars in Musculoskeletal Radiology, Vol. 1, No. 2, 1997 reports the treatment of a primary benign bone tumor and the management of concomitant pain using a percutaneously placed radiofrequency electrode, and is incorporated herein by reference. United States patents by E. R. Cosman and W. J. Rittman, III, entitled “Cool-Tip Electrode Thermal Surgery System,” U.S. Pat. No. 6,506,189 B1, date of patent Jan. 14, 2003, and “Cluster Ablation Electrode System,” U.S. Pat. No. 6,530,922 B1, date of patent Mar. 11, 2003, described systems and method related to tissue ablation with radiofrequency energy and electrodes and are hereby incorporated by reference herein in their entirety. Another example of probes for high-frequency tissue ablation includes microwave (MW) antennae. Another example of probes for tissue ablation are irreversible-electroporation (IRE) probes. Another example of probes for tissue ablation are cryogenic ablation probes.
Each Cosman CC cannula and RFK cannula, manufactured by Cosman Medical, Inc. in Burlington, Mass., includes a pointed metal shaft that is insulated except for an uninsulated electrode tip. The CC cannula has a straight shaft. The RFK cannula has a curved shaft; one advantage of a curved shaft is that it can facilitate maneuvering of the cannula's tip within tissue. Each cannula includes a removable stylet rod that can occlude the inner lumen of the cannula's shaft (which can, for example, facilitate insert of the cannula into solid tissue) and can be removed to allow for injection of fluids or insertion of instruments, like an electrode. Each cannula has a hub at its proximal end, the hub sized for manual manipulation of the cannula and having a luer port to accommodate an injection syringe or a thermocouple (TC) electrode, for example the Cosman CSK electrode, Cosman TCD electrode, and Cosman TCN electrode, that can deliver electrical signal output, such as RF voltage or stimulation, to the uninsulated cannula active tip and that can measure the temperature at the cannula active tip. The Cosman CSK and TCD electrodes have a shaft that is stainless steel. The Cosman TCN electrode has a shaft that is Nitinol. One CC or RFK cannula works with one CSK, TCD, or TCN electrode a two-piece RF electrode system configured for ablation of bodily tissue with temperature control. The Cosman CU electrode is an example of a one-piece RF electrode system wherein the electrode shaft has a tissue-piecing tip, insulation over the proximal shaft to produce an active electrode tip at the shaft distal end, a thermocouple temperature sensor with the active electrode tip, an injection port, a connection to an RF generator, and a lumen within the shaft to provide for fluid injection. The Cosman CR electrode is an example of a one-piece, tissue-piercing, radiofrequency, injection electrode that does not include a temperature sensor. The Cosman CP electrode is an example of a one-piece stimulation electrode system wherein the electrode shaft has a tissue-piecing tip, insulation over the proximal shaft to produce an active electrode tip at the shaft distal end, an injection port, a connection to an nerve-stimulation signal generator (which can be included in an RF generator, in some embodiments), and a lumen within the shaft to provide for fluid injection. Related information is given in Cosman Medical brochure “Four Electrode RF Generator”, brochure number 11682 rev A, copyright 2010, Cosman Medical, Inc., and is hereby incorporated by reference herein in its entirety.
It is desirable that an RF probe (which includes both unitized RF electrodes, and RF cannula that work with separate electrodes), a nerve-stimulation injection needle, a muscle-stimulation needle, a medical electrode, or another type of electrical medical probe having an electrically-insulated shaft and electrically-insulated hub are constructed such that there is no gap in the electrical insulation at the interface between the hub and the shaft. One reason that the lack of a hub-to-shaft insulation gap is desirable is the probe shaft can be inserted into tissue all the way up to the probe hub without risk that electrical current will flow from a conductive gap between the hub and shaft and thereby unintentionally heat, burn, stimulate, measure, or otherwise affect tissue at that location (such as skin in the case of percutaneously placed RF cannula, RF electrode,active electrode probe, or measurement electrode probe). In a first example in the prior art, avoiding an electrical-insulation gap at the hub-to-shaft interface of an RF probe is accomplished by first applying electrical insulation (such as by heating shrinking plastic heat shrink tubing over the shaft, or by spraying, painting, or dipping fluid insulation onto the shaft) over the metallic probe shaft, and then attaching the hub to shaft such that the hub covers both the shaft and the insulation (for example, by gluing the hub to the insulated shaft, or insert-molding the hub over the insulated shaft) such that there is no uninsulated gap between the hub and shaft that could contact tissue. One disadvantage of the said first example in the prior art, is that the insulation is attached to the shaft before the hub is attached to the shaft. Another disadvantage of the first example in the prior art, is the process of attaching the hub to the shaft must be designed to avoid damaging the insulation; for example, the process must have thermal, chemical, and physical characteristics that are not degrading to the insulation. In a second example in the prior art, avoiding an electrical-insulation gap at the hub-to-shaft interface of an RF probe is accomplished by first attaching the hub to the metallic shaft (for example by gluing or insert-molding), then applying the insulation to the shaft (such as by heating shrinking plastic heat shrink tubing over the shaft, or by spraying, painting, or dipping fluid insulation onto the shaft), and then covering any part of the metallic shaft that is not covered by the hub or the insulation at the hub-to-shaft interface (for example, applying glue between the shaft and hub, or precisely sliding the insulation along the shaft up to the hub). In the case where the electrical insulation is heat shrink tubing, application of the tubing to the shaft by heating it can cause the tubing to shrink both radially and longitudinally, and the longitudinal shrinkage of the insulation can leave part of the metallic shaft exposed unless the insulation is fixtured during shrinking or repositioned after shrinking. In the case where electrical insulation is applied to the shaft by spraying, painting or dipping inaccuracies in the process can lead to parts where the metallic shaft is exposed. One disadvantage of the said second example in the prior art is that an additional operation is performed to cover any gap in the insulation at the hub-to-shaft interface. Another disadvantage of the second example in the prior art is that greater precision, and often greater time, is required in the application of insulation to shaft to avoid gaps in the insulation at the hub-to-shaft interface.
The present invention overcomes the stated disadvantages and other limitations of the prior art.